Electromagnetic frictionally engaged clutch and method for operating the same

ABSTRACT

An electromagnetic frictionally engaged clutch for arranging inside a drive train connecting a drive motor and a vehicle door or flap. The arrangement ensures that the vehicle door is securely held in each intermediate position, when the clutch is in an idle state, while maintaining the possibility of a manual emergency actuation of the vehicle door. The rotor includes at least one permanent magnet in addition to the electric coil, such that when a current does not pass through the coil, the armature disk is pressed against the friction lining of the rotor, with a force which is strong enough for the vehicle door or vehicle flap to securely remain in position occupied when the clutch is an idle state, and for the friction engagement between the armature disk and the friction lining to be overcome when the vehicle door or vehicle flap is subsequently manually actuated.

The invention relates to an electromagnetic frictionally engaged clutchto be arranged within a drive train connecting a drive motor and avehicle door or a vehicle flap (tailgate, hood, etc.). The inventionrelates further to a method for operating such a clutch.

In motor vehicles having a vehicle door or vehicle flap which can beoperated automatically (in the following text, also designated only avehicle door for short), the vehicle door is closed or opened, forexample by the driver of the vehicle, by means of an appropriateoperation of a switch provided in the instrument panel. For thispurpose, the switching signal generated by the switch acts on anelectronic control device which, in turn, generates electric controlsignals for the activation of an electric motor which then, for itspart, pivots or displaces the vehicle door via a gear mechanism andfurther transmission elements connected downstream.

The disadvantage in the case of these known motor vehicles is, interalia, that when the vehicle door is pushed to manually, a highresistance has to be overcome because of the gear mechanism and electricmotor operatively connected to the vehicle door, and increased wear ofthese components occurs.

In order to avoid wear of this type, a vehicle door which can beoperated automatically has already been proposed, in which the motor orthe gear mechanism connected downstream of the motor can be uncoupledfrom the drive shaft operating the vehicle door by means of anelectromagnetic clutch, so that, when the clutch is disengaged, manualoperation of the vehicle door is possible without its movement beinginhibited by the structural units (for example electric motor orintermediate gear mechanism) arranged on the drive shaft of the clutch.

Electromagnetic clutches of this type are generally constructed asfrictionally engaged clutches and therefore comprise a rotor part whichis provided with a friction lining and firmly connected to a first shaftso as to rotate with it and on which, on its side facing away from thefriction lining, an electric coil is arranged, and an armature diskwhich is firmly connected to a second shaft so as to rotate with it butbe axially displaceable and which, when the clutch is engaged, is pulledagainst the friction lining of the rotor part of the first shaft andproduces a frictional connection between the two shafts. When the clutchis disengaged, the armature disk and the rotor part are forced apart bymeans of a spring, so that there is an accurately predefined gap-likedistance between armature disk and friction lining.

These clutches therefore have the disadvantage that, in the nonenergizedstate, because of the disengaged clutch, the vehicle door can be movedeasily and is frequently subjected in an uncontrolled manner to forcesacting on it (the force of gravity, springs of the suspension, dampers,etc.) when it is in an intermediate position between the closed and theopen position. Given the presence of an appropriately strong spring,tailgates are generally pivoted from the intermediate position into theopen end position after the clutch has been disengaged, although thevehicle door is frequently intended to remain in the respectiveintermediate position for safety reasons.

In German patent application number 101 52 697.0, which is not a priorpublication, a clutch has already been proposed by means of which thevehicle door can be held securely in any intermediate position when theclutch is in its disengaged state, and by means of which emergencymanual operation of the vehicle door is also possible. For this purpose,a resilient element, for example a compression spring, is provided,which acts on the armature disk of the clutch in the axial direction insuch a way that, when the clutch is disengaged, the armature disk ispressed against the friction lining of the rotor part with a force whichis sufficiently high for the vehicle door to remain securely in therespective position assumed when the clutch is disengaged. On the otherhand, in the event of subsequent manual operation of the vehicle door,it should be possible for the frictional connection between armaturedisk and friction lining to be overcome.

In the case of this clutch, it has proven to be disadvantageous that theexpenditure of a relatively great amount of force is necessary for themanual operation of the vehicle door.

The invention is based on the object of specifying an electromagneticfrictionally engaged clutch in which the vehicle door is held securelyin any intermediate position when the clutch is in its disengaged state,and which permits both emergency manual operation with the expenditureof force and operation of the vehicle door with only little manualexpenditure of force. Furthermore, a method for operating a clutch ofthis type is to be specified.

According to the invention, this object is achieved with regard to theclutch by the features of claim 1 and with regard to the method by thefeatures of claims 9 and 10. Further, particularly advantageous,refinements of the invention are disclosed by the subclaims.

The invention is based substantially on the idea of providing apermanent magnet which acts on the armature disk of the clutch in theaxial direction in such a way that, when the clutch is disengaged, thearmature disk is pressed against the friction lining of the rotor partwith a force which is high enough for the vehicle door to remainsecurely in the respective position assumed when the clutch isdisengaged and that, in the event of subsequent manual operation of thevehicle door, the frictional connection between armature disk andfriction lining can be overcome. In order to permit relatively easymanual operation of the vehicle door, current is applied to the coil insuch a way that its magnetic field is opposed to the magnetic field ofthe permanent magnet and the vehicle door can thus be moved by hand withvirtually no force.

It has proven to be advantageous if the armature disk is acted on in theaxial direction and pressed against the friction lining of the rotorpart by at least one resilient element (compression spring, disk spring,corrugated disk, rubber buffer, etc.) in addition to the magnetic forceof the permanent magnet.

In order to ensure a rotationally firm connection between armature diskand armature disk carrier with the simultaneous ability of the armaturedisk to be displaced axially, the armature disk carrier comprises axialguide parts which engage in corresponding groove-like recesses in thearmature disk.

Furthermore, it has proven to be expedient if, on its side facing awayfrom the friction lining, the rotor part has a recess in which the coilis at least partly arranged, the coil being mounted fixed to thehousing.

On its side facing the rotor part, the armature disk carrier can have asealing lip which extends over the entire circumference and protects thefriction lining of the rotor part against lubricants entering. Ofcourse, however, other seals, such as O-ings or felt parts, can also beused.

With the clutch according to the invention, it is possible in astraightforward manner to predefine a “transmission torque curve”, thatis to say the clutch can implement different transmission torques indifferent positions of the vehicle door, by means of predefining anappropriate voltage or current profile.

Further details and advantages of the invention emerge from thefollowing exemplary embodiments, explained by using figures, in which:

FIG. 1 shows a first exemplary embodiment of a clutch according to theinvention in a side view illustrated schematically, partly in section,and

FIG. 2 shows a further exemplary embodiment, corresponding to FIG. 1, ofa clutch according to the invention with spring assistance.

In FIG. 1, an electromagnetic frictionally engaged clutch is designatedby 1, being arranged within a drive train between a drive motor, notillustrated, and a tailgate, likewise not illustrated, of a motorvehicle.

The clutch 1 comprises a rotor part 4 which is provided with a frictionlining 2 and firmly connected to a first shaft 3 so as to rotate with it(for example the drive shaft connected to the drive motor), which, onits side facing away from the friction lining 2, has a recess 5 in whichan electric coil 6 is mounted fixed to the housing. The coil 6 isconnected to an electric control device 8 by electric leads 7.

The clutch 1 also has an armature disk 10 which is firmly connected to asecond shaft 9 (output shaft) so as to rotate with it but be axiallydisplaceable. For this purpose, the second shaft 9 is firmly connectedto an armature disk carrier 11, which comprises axial guide parts 12which engage in corresponding groove-like recesses 13 in the armaturedisk 10.

On its side facing the rotor part 4, the armature disk carrier 11 has asealing lip 14 which extends over the entire circumference, covers thefriction lining 2 of the rotor part 4 completely and prevents lubricantsbeing able to penetrate into this region.

Arranged on the rotor part 4, parallel to the electric coil 6, is apermanent magnet 15, which produces a magnetic field strength which isselected such that, when the coil 6 is not energized, the armature disk10 is pressed against the friction lining 2 with a predefined force andthe tailgate remains in the respective position assumed when the clutch1 is disengaged, on account of the frictional connection. However, itshould be possible for the frictional connection between armature disk10 and friction lining 2 to be overcome during the subsequent manualoperation (emergency operation) of the tailgate.

In the following text, the mode of action of the clutch 1 will beexplained:

If the tailgate (not illustrated) is to be opened, for example, theelectric coil 6 is energized by the control device 8. As a result, themagnetic force of the permanent magnet 15 is increased. If the firstshaft 3 is then driven by a drive motor, then the second shaft 9 iscarried along by the clutch 1 and operates the tailgate, notillustrated.

If, before reaching its end position, the tailgate is to be stopped in apredefined angular position, then the supply of current to the coil 6 isinterrupted by the control device 8. On account of the magnetic force ofthe permanent magnet 15, a frictional torque remains between thefriction lining 2 and the armature disk 10 and ensures that the tailgateremains securely in its assumed position. By means of appropriatelypowerful manual operation of the tailgate, the latter can then be closedagain or opened completely (emergency operation, for example in theevent of failure of the power supply).

On the other hand, if the tailgate is to be operated manually from apredefined position without the expenditure of great force, the electriccoil 6 is energized again, the direction of the current being selectedsuch that the magnetic field produced weakens the magnetic field of thepermanent magnet 15 and the tailgate can be actuated by hand withvirtually no force.

Of course, the invention is not restricted to the exemplary embodimentdescribed above. For example, in order to assist the permanent magnet15, a resilient element can additionally be provided which presses thearmature disk 10 against the rotor part 4 when the coil 6 is notenergized.

A corresponding exemplary embodiment of a clutch 20 of this type isillustrated in FIG. 2. In this case, the resilient elements (helicalcompression springs) designated by 21 are arranged in correspondingblind drilled holes 22 in the armature disk 10. Otherwise, theconstruction of this clutch 20 corresponds to the construction of theclutch 1 explained above by using FIG. 1.

LIST OF DESIGNATIONS

-   1 Clutch-   2 Friction lining-   3 First shaft-   4 Rotor part-   5 Recess-   6 Electric coil, coil-   7 Electric lead-   8 Control device-   9 Second shaft-   10 Armature disk-   11 Armature disk carrier-   12 Guide part-   13 Recess-   14 Sealing lip-   15 Permanent magnet-   20 Clutch-   21 Resilient element, compression spring-   22 Blind drilled hole

1. An electromagnetic frictionally engaged clutch to be arranged withina drive train connecting a drive motor and a vehicle door or a vehicleflap, having the following features: a) the clutch (1; 20) comprises arotor part (4) which is provided with a friction lining (2) and isfirmly connected to a first shaft (3) so as to rotate with it and, onits side facing away from the friction lining (2), an electric coil (6)is arranged, and an armature disk (10) which is firmly connected to asecond shaft (9) so as to rotate with it but can be displaced axially;b) arranged on the rotor part (4) in addition to the electric coil (6)is at least one permanent magnet (15), so that when the coil (6) is notenergized, the armature disk (10) is pressed against the friction lining(2) of the rotor part (4) with a force which is high enough for thevehicle door or vehicle flap to remain securely in the respectiveposition assumed when the clutch (1; 20) is disengaged and, duringsubsequent manual operation of the vehicle door or vehicle flap, thefrictional connection between armature disk (10) and friction lining (2)can be overcome.
 2. The clutch as claimed in claim 1, characterized inthat the armature disk (10) can be acted on in the axial direction by atleast one resilient element (21) in such a way that, when the coil (6)is not energized, on account of the permanent magnet (15) and theresilient element (21) together, the armature disk (10) is pressedagainst the friction lining (2) of the rotor part (4) with a force whichis high enough for the vehicle door or vehicle flap to remain securelyin the respective position assumed when the clutch (1; 20) is disengagedand, during subsequent manual operation of the vehicle door or vehicleflap, the frictional connection between armature disk (10) and frictionlining (2) can be overcome.
 3. The clutch as claimed in claim 2,characterized in that the resilient element (21) is a compressionspring, a disk spring, a corrugated disk or a rubber buffer.
 4. Theclutch as claimed in claim 1, characterized in that the second shaft (9)is firmly connected on the outside to an armature disk carrier (11) soas to rotate with it, the latter comprising axial guide parts (12) whichengage in corresponding groove-like recesses (13) in the armature disk(10).
 5. The clutch as claimed in claim 4, characterized in that thesecond shaft (9) or the armature disk carrier (11) contains at least oneopen blind drilled hole (22) on the side facing the armature disk (10)in order to accommodate the compression spring (21).
 6. The clutch asclaimed in claim 1, characterized in that, on its side facing away fromthe friction lining (2), the rotor part (4) has a recess (5) in whichthe coil (6) is at least partly arranged.
 7. The clutch as claimed inclaim 1, characterized in that the coil (6) is mounted fixed to thehousing.
 8. The clutch as claimed in one of claims 1 to 7, characterizedin that, on its side facing the rotor part (4), the armature diskcarrier (11) has a sealing lip (14) which extends over the entirecircumference and covers the friction lining (2) of the rotor part (4)completely.
 9. A method for operating the clutch as claimed in claim 1,characterized in that, in order to engage the clutch (1; 20), theelectric coil (6) has applied to it a current which causes a magneticfield oriented in the same direction as the magnetic field of thepermanent magnet (15), so that the armature disk (10) is pressed firmlyagainst the friction lining (2) of the rotor part (4), and in that, inorder to disengage the clutch (1; 20), the electric coil (6) has appliedto it a current which produces a magnetic field oriented in the oppositedirection to the magnetic field of the permanent magnet (15), so thatthe armature disk (10) is not pressed or pressed only loosely againstthe friction lining (2) of the rotor part (4).
 10. The method as claimedin claim 9, characterized in that the electric coil (6) has a currentapplied to it which has a value dependent on the respective position ofthe vehicle door or vehicle flap.